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Dear Alan, LF Group,
The fluted ferrite rods are probably "impeder rods"
- these are used for induction welding of the seams in metal tubing produced by
rolling strip metal. They fit inside the tube at the point where the weld is
being made. Their purpose is to force the induced current to flow through the
weld, rather than around the circumference of the tube; there is a fairly good
description at:
The purose of the flutes is to allow the
circulation of cooling water, allthough it may also be significant in reducing
eddy currents. My old Philips ferrite data book lists these as
available in either 3C85 or 3D3 (a somewhat lower permeability ferrite otherwise
similar to 3C85). The induction welding application normally operates in
the LF/MF range at the 10s of kW level - potentially these might be useful in an
LF TX loading coil application, if a coil using them can be made with high
enough Q...
Cheers, Jim Moritz
73 de M0BMU
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